1. Field of the Invention
The present invention relates to an image processing apparatus that uses colored ink and image enhancing liquid to print an image on a print medium. In particular, the present invention relates to a technique for, in the case of using ink contained pigment as color material, improving gloss unevenness within an image.
2. Description of the Related Art
In the past, there has been widely known an ink jet printing apparatus that uses dye ink to enable the formation of a high-quality image having high color reproducibility. On the other hand, in recent years, the need for an ink jet printing apparatus using pigment ink having higher image fastness than the dye ink has been increasing. However, the pigment ink has a problem that color material tends to be unlikely to permeate into a print medium, and therefore in particular, in the case of printing on a glossy print medium, a degree of gloss is different between a print part and a non-print part of an image, and therefore gloss unevenness is likely to occur.
For such a problem of gloss unevenness, for example, there is invented a method that laminates a transparent film on a print surface. Also, there is proposed a method that adds an additive such as titanium dioxide to colored ink.
On the other hand, Japanese Patent Laid-Open No. 2002-307755 discloses a method that, in addition to pigment ink, uses colorless and transparent, or white colored image enhancing liquid to form an image. According to Japanese Patent Laid-Open No. 2002-307755, there is disclosed a method that detects print or non-print of the pigment ink on a pixel basis to print the image enhancing liquid on non-print pixels, and thereby conforms glossiness of pixels printed with the image enhancing liquid to glossiness of pixels printed with the pigment ink to reduce gloss unevenness.
However, in the method that laminates the transparent film, a laminate mechanism is required, so that an apparatus is increased in size, and to do the laminating work, time and effort are spent. Also, in the method that adds the additive such as titanium dioxide to the colored ink, ejection stability in a print head becomes a problem.
As disclosed in Japanese Patent Laid-Open No. 2002-307755, the method that applies the image enhancing liquid on areas where the colored ink is not printed can make a sense of glossiness nearly uniform at some gradations but may not sufficiently solve the gloss unevenness depending on a gradation. This is because the gloss unevenness perceived by a person is influenced not only by glossiness of printed material but also by image clarity of the printed material, and therefore difference in image clarity appears between the highlight areas where the colored ink is hardly applied and dark areas where a large amount of colored ink is applied, for example. That is, unless both of the glossiness and the image clarity are nearly uniform, the gloss unevenness may be perceived.